The present invention relates to a nonwoven having a filament density pattern yielding low tensile strength and high percent elongation in a first direction (e.g., CD) and high tensile strength and low percent elongation in a second direction (e.g., MD), and a method of making such a nonwoven.
Spunbond nonwoven fabrics are made of continuous strands or filaments that are laid down on a moving conveyor belt in a randomized distribution. In a typical spunbond process, resin pellets are processed under heat to a melt and then fed through a spinnerette to create hundreds of thin filaments or threads. Jets of air cause the threads to be elongated, and the threads are then blown onto a moving web where they are laid down and sucked against the web in a random pattern to create a fabric. The filament density of the fabric is typically fairly uniform and symmetrically extending in both the machine direction (MD) and the cross direction (CD) (at least this is the goal). The fabric then passes through a bonding station. Bonding is necessary because the filaments or threads are not woven together.
Other nonwoven fabrics include fabrics made from staple fibers, meltblown fibers, carded fibers and and short cut fibers. As used herein the terms "spun fibers" and "fibers" include the spun filaments described above as well as staple fibers, meltblown fibers, carded fibers and and short cut fibers.
A non-uniform and non-symmetrical fiber density pattern could result in a fabric with an expected elongation in one direction (e.g., MD), but an unexpected increased elongation in the other direction (e.g., CD). This is desired in situations where minimal elongation is required in the machine direction and yet high elongation is required in the cross direction. For example, any elongation in the machine direction will disrupt the converting machines that are used to make diapers, while substantial elongation in the cross direction is desired to give each individual diaper some give around the wearer's waist.
Accordingly, it is an object of the present invention to provide a nonwoven fabric having a non-uniform fiber density pattern and a method of making such fabric.
Another object of the present invention is to provide a nonwoven fabric and method of making same wherein the fabric is highly extensible in a first direction (typically the CD) as compared to a second direction (typically the MD).
Another object of the present invention is to provide a nonwoven fabric and method of making same wherein the fibers of the fabric are oriented more in the MD than in the CD thereby providing higher tensile strength in the MD than in the CD.
Another object is to provide such a method and fabric wherein the nonwoven fabric has low tensile strength and high percent elongation in the first direction (typically the CD), and high tensile strength and low percent elongation in the second direction (typically the MD).
It is a further object to provide such a method and fabric wherein the density of the fibers in the fabric varies between strips of relatively high density and strips of relatively low density, the strips extending substantially continuously along the length of the fabric in the machine direction in an alternating pattern.
It is a still further object of the invention to provide such a fabric wherein less fibers are bonded together in the strips of relatively low fiber density than in the strips of relatively high fiber density.
It is a still further object of the invention to provide such a fabric which provides increase liquid wicking in the strips of relatively high fiber density and increased liquid strike-through in the strips of relatively lower fiber density.
It is a still further object of the invention to provide such a fabric which has a shrinkage differential between the strips of relatively high fiber density and the strips of relatively lower fiber density when the fabric is exposed to heat, with greater shrinkage in the strips of relatively high fiber density.
It is also an object of the present invention to provide such a method which is simple and economical to use and maintain.